Process for obtaining thiocyanates of the alkaline-earth metals



Patented Mar. 18, 1930 UNITED STATES PATENT "orics ROBERT E. FULTON, OF WILKINSIBURG, PENNSYLVANIA, .ASSIGNOR TO THE ZKOPIPERS COMPANY, A CORPORATION PENNSYLVANIA.

PROCESS FOR OBTAINING THIOCYANATES OF THE. ALKALINE-EARTH No Drawing.

My invention relates to a process for obtaining alkaline earth metal thiocyanate from complex liquors, such as gas purification liquors produced in the treatment of fuel gas with alkaline absorbent liquids for the removal of acidic constituents. In general, such liquors contain sodium thiocyanate, sodium thiosulphate, sodium carbonate, sod1um bicarbonate and sodium ferrocyanide 1n vary, ing amounts, and also colloidal and suspended matter, coloring matter, dirt, etc.

An object of my invention is to provide a process of treating a liquor of the character indicated aboveto obtain a valuable product therefrom. I

A second object of my invention is to provide a process of obtaining alkaline earth metal thiocyanate in substantially pure form from a crude and complex liquor. Y

A further object of my invention is to accomplish the conversion of undesirable soluble constituents of gas purification liquor into insoluble materials capable of being separated from the desired product by a simple operation.

A further object of my invention is to provide a process of removing a soluble foreign material such as sodium chloride from a solu-- tion of alkaline earth metal thiocyanate.

A still further object of my invention is to provide a process of removing colloidal matter, coloring matter and dirt from a solution of alkaline earth metal thiocyanate.

My invention has for further objects such other operative advantages or results -as may hereinafter be found to obtain.

In the specific instance which will be described hereinbelow, my invention is described with reference tothe preparation of alkaline earth metal thioc anate from a gas purification liquor in which the various salts, such as the thiocyanate, thiosulphate and carbonate, are combined with sodium. This process requires a preliminary conversion of such sodium salts to alkaline earth metal salts. However,my invention is not limited to the treatment of liquors containing-principally sodium compounds but may be applied to other alkali compounds, or to liquors which consist originally of alkaline earth metal Application filed December 23, 1926. Serial No. 155,756.

general character indisuch as calcium, magnesium, or the like. For

convenience, however, the description will henceforth be limited to the preparation of calcium thiocyanate, it being understood that other alkaline earth metal and thiocyanates maydbe correspondingly recovered or prepare In practicing my invention, I may treat the liquor from a gas purification process directly, but I prefer to start with such a liquor after it has been treated by any suitable process for the removal of most of the thiosulphate therefrom.

I An example of such a liquor is illustrated by the following analysis:

Sodium thiocyanate (NaCNS) 700 grams per liter. Sodium thiosulphate (P11128203) 200 grams per liter. Sodium carbonate (Nflgcog) 12 grams per liter. Sodium terrocyanlde (Na.Fe(CN) 34 grams perliter.

(Jolloidulmatter, coloring matter, dirt,

eh Present.

treatment, the sodium thiocyanate will be converted to calcium thiocyanate and the sodium thiosulphate will, of course, be convert- A ed to calcium thiosulphate.' The solubility of the latter is so near to that of the calcium thiocyanate that separation of these two materials by ordinary means is diflicult and tedious'. I have discovered that, if the liquor after treatment with the' calcium salt is heated to near the boiling point, the calcium thio sulphate will be decomposed, with resultant formation of the almost completely insoluble calcium sulphite and sulphur. This reaction probably proceeds as follows:

etc., may now be removed by filtration. The filtrate is a clear and nearly pure solutlon of calcium thiocyanate and may be concentrated without further treatment to yield crude crystalline calcium thiocyanate. When it is desired to remove the small amounts of salt, colloidal matter, coloring matter, dirt, etc., present in the liquor as obtained above, I treat the solution with'an agent capable of oxidizing, bleaching, or pre cipitating the colloidal matter, coloring matter and dirt. Suchagents, for convenience, and since their use isunderstood, Wlll here- 1 Y inafter be designated as precipitants, but

this term as hereinafter used is not to be con-.

strued to mean an agent capable of efiecting a precipitation alone. I also concentrate the solution to'such a point that sodium chloride is precipitated and may be removed by simple filtration. The order of the steps may be a reversed, according to the desired results, the

nature of the precipitant, etc.

In order that my invention may be clearly set forth and understood,'I will now describe,

with reference to the treatment of the particular as purification liquor recited above, the preerred manner in which it is accomplished and performed.

A convenient wei ht of liquor of known composition is heated to a temperature of 60 to 70 C. in a suitable reaction vessel, preferably equipped with a heating jacket or coils and a stirring device. To it 'is added a consome insoluble ferrocyanide.

In addition to the calculated amount, an excess of 2% of calcium chloride is added, to insure complete reaction. Before adding the calcium chloride solution, itsis preferably heated to from 100 to 105 C. and

it is then added slowly to the heated liquor. The temperature of the reaction mixture ,is now increased to from 110 to 120 C. and

maintained within this range for about one hour, during which period of time the heavy viscous mass is agitatedconstantly. While itis preferred to allow one hour for the reaction to be completed, in many instances, the reaction may be completed at the end of 30 minutes and, in others, it may be necessary to maintain this temperature for a longer period than one hour. However, this is within the discretion of the operator. During the said reaction period, the conversion of calcium thiosulphate to calcium sulphite and sulphur is accomplished.

The reaction mixture is now cooled to a temperature preferably below 59 C. and

filtered in any suitable manner. The precipitate or filter cake consists of sodium chloride, calcium carbonate, calcium sulphite, sulphur, sodium calcium ferrocyanide, and some coloring matter and dirt, and is discarded or fur- "ther treated by any suitable process for recovery of its constituents. The filtrate, in addition to calcium thiocyanate, also contains some sodium chloride and small'amounts of coloring and colloidal matter. I further treat 7 this filtrate, asindicated above, with a precipitant for oxidation and/or precipitation of coloring and colloidal matter; and. separately for the removal of sodium chloride I may use various precipitants, such as milk of lime, bleaching powder, sodium perborate, chlorine water, hydrogen peroxide orthe like,

either alone or in combination with ,others,

and, according to the specific precipitant used and the result desired, the procedure will be I varied. For this reason, I will recite various examples of the purification of this crude calcium thiocyanate liquor.

Example I By adding water, the specific gravity of the crude calcium thiocyanate solution is reduced to between 1.22 and 1.25. It is then treated at ordinary temperatures with a predetermined quantity of milk of lime, agitated for from 15 to 30 minutes, and then filtered. The lime should be suspended in such a quantity of water that the specific gravity of the treated solution does not fall below 1.2 at 25 C. for the reason that, at about this specific gravity, the calcium hydroxide is least soluble in the calcium thiocyanate solution and may subsequently be su stantially completely removed therefrom.

The filtrate from the above filtration operatlon, consisting principally of calcium thiocyanate and containing also sodium chloride, is now evaporated, preferably in vacuo, to a specific gravity equivalent to from 1.4 to 1.41 at 25 C. and cooled to below 40"v C. At th1s temperature and concentration,

the sodium chloride is practically insoluble in the calcium thiocyanate solution. The solution is then filtered to remove said sodium chloride. The filtrate is now a substantially pure solution of calcium thiocyanate and may e further concentrated to ield crystalline calcium thiocyanate Ca (CNg) -3H O.

Example II.

The crude calcium thiocyanate liquor is evaporated to a specific gravity equivalent to 1.4 to 1.41 at 25 C. and cooled to below 40 C. The sodium chloride precipitates and is removed by filtration. The filtrate, containing calcium thiocyanate, coloring matter and col- Ill.

loidal matter, is now treated with a solution of bleaching powder in predetermined quantity, heated to a temperature of from 90 C. to 100 (1, and maintained at this temperature for from 20 to 30 minutes with agita- 20)- Ewample 111 When the complete removal of sodium chloride is not necessary, the crude calcium thiocyanate solution may be treated directly with a precipitant, such as bleaching powder, evaporated to a specific gravity equivalent to 1.4 to 1.41 at 25 C., cooled to below 40 C. and filtered. This filtration will remove the colloidal and coloring matter and most of the sodium chloride and the filtrate may be concentrated to yield nearly pure calcium thiocyanate, although, as indicated above, this product will still contain very small amounts of sodium chloride.

In any of the filtration steps described above, any of the various well-known sup lementary means, such as activated car on, silica-gel, fullers earth, calcined alumina, and the like may be used in conjunction with the filtration to yield a very pure and lightcolored calcium thiocyanate.

My invention has numerous advantages which will easily appear from the foregoin and from a comparison with the prior art. provide a process for obtaining a substantially pure calcium thiocyanate in a simple manner without elaborate purification and crystallization steps and from a cheap and .com-

plex raw materialin fact, a waste product.-

containing large quantities of salts other than the sodium thiocyanate from which the calcium thiocyanate is prepared. The apparatus, reagents, and time required for the preparation of substantially pure calcium thiocyanate, according to my process, are all cheapened or reduced to a very advantageous point.

While my invention is hereinabove described with reference to the treatment of a.

particular material and including certain specific examples by way of illustration, it may otherwise be embodied or practiced Within the scope of the claims hereinafter made.

I claim as'my invention:

1. The process of obtaining a solut1on of alkaline earth metal thiocyanate from gas purification liquor which comprises treating the liquor with a soluble alkaline earth metal salt, heating the mixture to near the bo ling point, allowing it to cool and removing insoluble material therefrom. I

2. The process of obtaining a solution of alkaline earth metal thiocyanate from gas purification liquor which comprises treating above 110 the liquor with a soluble alkaline earth metal salt, heating the mixture to such a point that alkaline earth metal thiosulphate present is decomposed and subsequently removing insoluble material therefrom.

3. The process of obtaining a solution of alkaline earth metal thiocyanate from gas purification liquor which comprises treatin the liquor with a soluble alkaline earth meta salt, heatin the mixture to a temperature 6, allowing it to cool and removing insoluble material therefrom.

4. The process of obtaining a solution of alkaline earth metal thiocyanate from gas purification liquor which comprises heating and agitating the liquor in the presence of alkaline earth metal chloride at a temperametal thiocyanate from gas purification liquor which comprises treating the liquor with a soluble alkaline earth metal salt, heating the liquor to near the boiling point, cooling and filtering the liquor to remove insolubles and subsequently treating the filtrate to re- ;over alkaline earth metal thiocyanate thererom. I

7. The process of obtaining alkaline earth metal thiocyanate from gas-purification liquor which com rises treating the liquor with a soluble alka ine earth metal salt, heating the liquor to near the boiling point, cooling and filtering it toremove insolubles, treating the filtrate with a reagent capable of precipitating colloidal and coloring matter, re-filtering the liquor to remove such precipitate and treating the filtrate to recover alkaline earth metal thiocyanate therefrom.

v8. The process of obtaining alkaline earth metal thiocyanate from gas purification liquor which comprises treating the liquor with a soluble alkaline earth metal salt, heating the liquor to near the boiling point, cooling and. filtering it to remove insolubles, treatingv the filtrate with a reagent capable of precipitating colloidal and coloring matter, while maintaining the liquid at a specific gravity of from 1.22 to 1.25, re-filtering the liquor to remove such precipitate and subsequentl treating the filtrate to recover alkaline eart metal thiocyanate therefrom.

' 9. The process of obtaining alkaline earth metal thiocyanate from gas purification liq; uor which Comprises treating the liquor wit a soluble alkaline earth metal salt, heating the liquor to near the boiling point, cooling and filtering it to remove insolubles, treating the filtrate with a reagent capable of preci itating colloidal and coloring matter, re- 1- tering the liquor to remove the precipitate thus formed, evaporating the filtrate to a specific gravity of approximately 1.4, allowlng it to cool, filtering it to remove insolubles and evaporating the filtrate to recover alkaline earth metal thiocyanate.

10. The process of obtaining a solution of calcium thiocyanate from gas purification liquor which comprises treatin the liquor with a soluble calcium salt, heating the mixture to such a point that calcium thiosulphate present is decomposed and subsequently removing insoluble material therefrom.

In testimony whereof, I have hereunto subscribed my name this 22nd day of December,

ROBERT R. FULTON. 

